The crystal structure of Ba4Ti10Al2O27 has been refined in a joint Rietveld refinement using neutron and X-ray powder data. The compound crystallizes in the monoclinic space group C2/m, with a=19.7057(3), b=11.3575(2), c=9.8318(2) Å, β=109.218(1)°, and V=2077.81(5) Å3. It is isostructural to Ba4Ti10Fe2O27 and Ba4Ti11ZnO27, and consists of a complex network of corner- and edge-sharing Ti/Al octahedra. The structure can best be described based on close-packed O/Ba-O layers in an 8-layer (8L) chhcchhc sequence. Out of a total of ten Ti/Al sites, Al was found to substitute for Ti mainly in four sites, and the remaining six sites were predominantly occupied by Ti. The unit cell contents derived from the refined site occupancies are Ba16Ti40.48Al7.52O108, essentially identical to the expected Ba16Ti40Al8O108. A reference diffraction pattern of this phase is also reported.

A system enabling X-ray diffraction patterns under controlled conditions of relative humidity and temperature has been devised and combined with an X-ray powder diffractometer. Relative humidity in the sample space is controlled by mixing dry N2 gas with saturated water vapor. Temperatures of the sample and inner wall of the sample chamber are monitored by two attached thermocouples and the information was fed back to the control unit. Relative humidity between 0% and the 95%, and temperature between room temperature and 60 °C can be controlled. All parameters including those for XRD are programmable and the system runs automatically. The function of the system was checked by recording the XRD patterns of montmorillonite (a clay mineral) and NaCl under increasing and decreasing relative humidity.

The following new or updated patterns are submitted by the JCPDS Research Associateship at the National Bureau of Standards. The patterns are a continuation of the series of standard X-ray diffraction powder patterns published previously in the NBS Circular 539, the NBS Monograph 25, and in this journal. The methods of producing these reference patterns are described in this journal, Vol. 1, No. 1, p. 40 (1986).

The data for each phase apply to the specific sample described. A sample was mixed with one or two internal standards: silicon (SRM640a), silver, tungsten, or fluorophlogopite (SRM675). Expected 2-theta values for these standards are specified in the methods described (ibid.). Data, from which the reported 2-theta values were determined, were measured with a computer controlled diffractometer. Computer programs were used to locate peak positions and calibrate the patterns as well as to perform variable indexing and least squares cell refinement.

Combining the exhaustive indexing of triclinic powder diffraction patterns with a crystallographic determination of unit cell parameters from pinacoid and prism reflections yields unit cell parameters with realistic limits of error. Additionally a referee method has been developed by which the six reciprocal cell parameters of a triclinic phase are determined by solving an exhaustive set of linear simultaneous equations in six unknowns.

That very large famous and infamous borough of New York City, namesake of one of the country's most graceful bridges, Brooklyn, was perhaps the least likely of places for the development of a teaching center of international brilliance – and, at that, in the then little known field of X-ray diffraction. Such was the case, however. Where else, it has been asked, could a visiting lecturer on X-ray technique look out at his audience and, to his dismay, find in the front row, Paul P. Ewald, Herman Mark, Isidor Fankuchen and David Harker – respectively, a founding father of X-ray diffraction, a founding father of polymer chemistry, an entrepreneur par excellence in X-ray crystallography, and a major player in macromolecular (proteins) analysis. Only there at the Brooklyn Polytechnic Institute. It was unique in its time and function as the pre-eminent school of learning for the rapidly evolving practices of polymer science and X-ray diffraction.

X-ray powder-diffraction data were collected for a new iron phosphate, Fe(PO4)·0.5H2O, obtained by reducing FePO4 with oxalic acid at 220 °C in the presence of water vapor and oxygen. The crystal system was determined to be orthorhombic with unit-cell parameters a=15.991(6) Å, b=20.156(7) Å, and c=7.223(2) Å.

X-ray powder patterns for the phases in the CaO-SrO-PbO ternary system, along with the corresponding crystal structures, were obtained from the literature and from the Powder Diffraction File. Available XRD patterns were compared with each other and with a simulated pattern for each phase, yielding a recommended reference pattern. The simulated powder patterns presented here deal with the phases found within the (Ca,Sr)2PbO4solid solution series and are recommended for the Powder Diffraction File (PDF).

New ternary compounds of Ca14Al10Zn6O35 and Ca3Al4ZnO10 compositions have been synthesized in the CaO–Al2O3–ZnO system. Single crystals of the new compounds have been grown, and crystal structures and crystallochemical properties were established. The phenomenon of heterovalence isomorphous statistical substitution of aluminium for zinc in alumino-oxygen tetrahedra has been established. It is now possible to synthesize a large group of new ternary compounds, the compositions of which are similar to that of spinels. The structure and properties of the new phases are presented.© 1997 International Center for Diffraction Data.

The capability of whole-powder-pattern decomposition in the quantitative phase analysis (QPA) of natural products was investigated using three- to six-component mixtures and pottery bodies. Here, the term pottery body means plastic clay suitable for making pottery and it is compounded of ceramic raw materials. Average errors of the weight fractions for each phase were within 1 weight percent in each mixture of natural products. The amounts of reduced oxides in pottery bodies derived from the X-ray diffraction technique were in good agreement with results obtained by X-ray fluorescence analysis. The present procedure does not require knowledge of crystal structures; it appears adequate for the QPA of natural products.

The crystal structure of the natural zeolite garronite from Goble, Oregon has been refined using high resolution synchrotron X-ray powder diffraction data. Garronite has the same tetrahedral aluminosilicate framework as gismondine [GIS], and earlier structural models indicated a strong tetragonal pseudosymmetry. Proposed models in the literature were based on the I4¯m2 and I41/a space groups, on account of symmetry lowering from the topological I41/amd space due to partial cation/water molecule order in the zeolitic cavities. Test structure analysis has been performed in all possible space subgroups including monoclinic space groups, and the refinement has been successfully carried out in space group I2/a (C2/c). The resulting monoclinic structure model is to be preferred over the tetragonal ones on the basis of: (1) lower agreement indices of the refinement; (2) a chemically sound framework geometry; and (3) a more satisfactory interpretation of the Ca atoms coordination in the extraframework cages.

Most modern X-ray powder diffraction work is carried out using the parafocusing powder diffractometer. The typical instrument employs a mechanical goniometer to control the basic geometric movements required for recording diffraction data. Modern trends toward high speed data acquisition and computerized analytical procedures make the need for a well designed and well maintained goniometer system increasingly critical. This paper reviews the mechanical design parameters of typical goniometer systems in light of their influence on the accuracy and precision obtainable in diffraction data. Data on typical vertical and horizontal goniometer systems are compared, along with bench tests using a state of the art “anti-backlash” gearing system. By examining the nature of the errors typically encountered in today's goniometers it becomes evident why the next major improvement will likely be in software rather than hardware.

Two complexes of gallium with 3-hydroxy-4-pyrones were synthesized as potential pharmaceutical compounds for oral administration. These compounds were analyzed by powder X-ray diffraction followed by computer indexing of the data. The first compound, tris(3-hydroxy-2-methyl-4-pyronato)gallium [Ga(C6H5O3)3], was found to be orthorhombic, a = 18.500(2), b = 16.948(2), c = 12.012(2) Å, V = 3766(1) Å3, Z = 8, Dm = 1.56(5), Dx = 1.570. The compound appears closely analogous to a similar compound containing Al instead of Ga, which crystallizes in space group Pbca. The second compound, tris(3-hydroxy-2-ethyl-4-pyronato)gallium [Ga(C7H7O3)3], was found to be monoclinic, a = 31.634(2), b = 8.7662(5), c = 7.8982(5) Å, β = 103.240(6)°, V = 2132.0(5) Å3, Z = 4, Dm = 1.50(5), Dx = 1.517, with a primitive space group.

Pentastrontium bromidephosphate, Sr5(PO4)3Br, was prepared by solid state reaction. The crystal structure of polycrystalline Sr5(PO4)3Br was refined from X-ray powder diffraction data by the Rietveld method using the structure model of Sr5(PO4)3Cl single crystals. Sr5(PO4)3Br is isostructural with Sr5(PO4)3Cl. The space group is P63/m. The cell parameters are a0=9.9641(1) Å, c0=7.2070(1) Å, α=β=90°, γ=120°, Z=2, d(calc)=4.27 g/cm3, and d(expt)=4.10 g/cm3. Atomic parameters are given. Final values are Rp=10.9%, Rwp=14.3%, and S=1.28. The figure of merit is F30=58 (0.013, 39).

The X-ray powder diffraction pattern of the room temperature phase of Cd4GeSe6, a II4 □ IV VI6 semiconducting material, has been recorded and evaluated. This material crystallizes in the monoclinic space group Cc [No. 9] with a=12.847(3), b=7.407(2), c=12.854(2) Å, β=109.82(1)°, and Z=4. The powder diffraction pattern was also used to refine the crystal structure of this material employing the Rietveld method. The refinement of 56 parameters led to RWP=13.2%, RP=9.95% for 3751 step intensities and RB=7.05% and RF=5.20% for 833 reflections. Cd4GeSe6 can be considered a defect “adamantane-structure” material with a sphalerite-related superstructure.